Nature of the Reactants and Influence of Water on the Supramolecular Assembly

The three novel, multi-nickel-substituted heteropolytungstates [Ni6As3W24O94(H2O)2]^17- (1), [Ni3Na(H2O)2(AsW9O34)2]^11- (2), and [Ni4Mn2P3W24O94(H2O)2]^17- (3) have been synthesized and characterized by IR, elemental analysis, electrochemistry, and magnetic studies. Single-crystal X-ray analysis was carried out on Na16.5Ni0.25[Ni6As3W24O94(H2O)2]·54H2O, which crystallizes in the triclinic system, space group P, with a = 17.450(4) (angstrom), b = 17.476(4) (angstrom), c = 22.232(4) (angstrom), = 85.73(3), = 89.74(3), = 84.33(3), and Z = 2, Na11[Ni3Na(H2O)2(AsW9O34)2]·30.5H2O, which crystallizes in the triclinic system, space group P, with a = 12.228(2) (angstrom), b = 16.743(3) (angstrom), c = 23.342(5) (angstrom), (alpha)= 78.50(3),(beta)= 80.69(3), (gamma)= 78.66 (3), and Z = 2, and Na17[Ni4Mn2P3W24O94(H2O)2]·50.5H2O, which crystallizes in the monoclinic system, space group P21/c, with a = 17.540(4) (angstrom), b = 22.303(5) (angstrom), c = 35.067(7) (angstrom),(beta)= 95.87(3) (angstrom), and Z = 4. Polyanion 1 consists of two B-(alpha)-(Ni3AsW9O40) Keggin moieties linked via a unique AsW6O16 fragment, leading to a banana-shaped structure with C2v symmetry. The mixed-metal tungstophosphate 3 is isostructural with 1. Polyanion 2 consists of two lacunary B-(alpha)-[AsW9O34]^9Keggin moieties linked via three nickel(II) centers and a sodium ion. Electrochemical studies show that 1-3 exhibit a unique and reproducible voltammetric pattern and that all three compounds are stable in a large pH range. An investigation of the magnetic properties of 1-3 indicates that the exchange interactions within the trimetal clusters are ferromagnetic. However, for 1 and 3 intra- and intermolecular interactions between different trinuclear clusters are also present.